The role of the S30 ribosomal subunit in controlling ambiguity in translation will be analyzed by: (a) the study of the tRNA-ribosome interaction at the topographical level; (b) the search of S30 mutations restricting ambiguity other than those in protein S12; and (c) the study of ambiguity in frameshift mutations. The postulated role of the S30 ribosomal subunit in controlling gene expression will be studied by analyzing whether pleiotropic ribosomal mutants have selectively lost the ability to translate some messenger RNAs. The structure of S16 RNA (the RNA component of the S30 subunit) and that of its precursors will be studied in relation to the mode of action of streptomycin by testing for their ability to specifically bind this drug.